Nonvolatile semiconductor memory apparatus and manufacturing method thereof

ABSTRACT

A nonvolatile semiconductor memory apparatus ( 10 ) of the present invention comprises a substrate ( 10 ), lower-layer electrode wires ( 15 ) provided on the substrate ( 11 ), an interlayer insulating layer ( 16 ) which is disposed on the substrate ( 11 ) including the lower-layer electrode wires ( 15 ) and is provided with contact holes at locations respectively opposite to the lower-layer electrode wires ( 15 ), resistance variable layers ( 18 ) which are respectively connected to the lower-layer electrode wires ( 15 ); and non-ohmic devices ( 20 ) which are respectively provided on the resistance variable layers ( 18 ) such that the non-ohmic devices are respectively connected to the resistance variable layers ( 18 ). The non-ohmic devices ( 20 ) each has a laminated-layer structure including plural semiconductor layers, a laminated-layer structure including a metal electrode layer and an insulator layer, or a laminated-layer structure including a metal electrode layer and a semiconductor layer. One layer of the laminated-layer structure is embedded to fill each of the contact holes and the semiconductor layer or the insulator layer which is the other layer of the laminated-layer structure has a larger area than an opening of each of the contact holes and is provided on the interlayer insulating layer ( 16 ).

RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. §371 ofInternational Application No. PCT/JP2007/071962, filed on Nov. 13, 2007,which in turn claims the benefit of Japanese Application No.2006-312590, filed on Nov. 20, 2006, the disclosures of whichApplications are incorporated by reference herein.

TECHNICAL FIELD

The present invention relates to a cross-point nonvolatile semiconductormemory apparatus using a resistance variable layer. Particularly, thepresent invention relates to a configuration in which a diode isincorporated to be connected in series with the resistance variablelayer.

BACKGROUND ART

In recent advancement of digital technologies in electronic hardware,larger-capacity and nonvolatile semiconductor memory apparatuses havebeen vigorously developed in order to store data of music, images,information and so on. For example, nonvolatile semiconductor memoryapparatuses using ferroelectric substances as capacitive elements arenow used in various fields. Furthermore, in contrast to the nonvolatilememory apparatus using the ferroelectric capacitors, a nonvolatilesemiconductor memory apparatus (hereinafter referred to as ReRAM) usinga material whose resistance value changes according to electric pulsesapplied and continues to keep its state has attracted an attentionbecause it can easily have compatibility with a normal semiconductorprocess.

For example, there is disclosed an apparatus configuration, for enablingthe use of the existing DRAM step as it is, in a ReRAM including onetransistor and one memory portion (see, e.g., patent document 1). TheReRAM includes transistors and nonvolatile memory portions connected todrains of the transistors. The memory portion has a structure in which aresistance variable layer whose resistance reversibly changes accordingto current pulses applied is sandwiched between an upper electrode and alower electrode. As the resistance variable layer, a nickel oxide (NiO),a vanadium oxide (V₂O₅), a zinc oxide (ZnO), a niobium oxide (Nb₂O₅), atitanium oxide (TiO₂), a tungsten oxide (WO₃), a cobalt oxide (CoO), etcis used. It is known that the transition metal oxide is allowed to havea specified resistance value by application of a voltage or currenthaving a threshold or higher and to hold the resistance value until thetransition metal oxide is newly applied with a voltage or current. And,the transition metal oxide can be manufactured using the existing DRAMstep as it is.

The above illustrated example includes one transistor and onenonvolatile memory portion. Also, a cross-point ReRAM using a perovskitestructure material is also disclosed (see, e.g., patent document 2).This ReRAM has a structure in which stripe-shaped lower electrodes areprovided on a substrate and an active layer is provided so as to coverthe entire surface of the lower electrodes. As the active layer, aresistance variable layer whose resistance reversibly changes accordingto electric pulses is used. On the active layer, stripe-shaped upperelectrodes are provided to respectively cross the lower electrodes at aright angle. A region where each of the lower electrodes and each of theupper electrodes cross each other such that the active layer issandwiched between the lower electrode and the upper electrode forms amemory portion. The lower electrodes and the upper electrodes serve asword lines or bit lines. With such a cross-point configuration, a largercapacity is attainable.

In the cross-point ReRAM, a diode is incorporated into the ReRAM suchthat the diode is connected in series with the resistance variable layerto avoid the influence from the resistance variable layers on anotherrows or columns, when reading the resistance value of the resistancevariable layer provided at the cross-point.

For example, a ReRAM is disclosed, which comprises a substrate includingtwo or more bit lines arranged to extend at parallel intervals, two ormore word lines arranged to extend at parallel intervals and to crossthe bit lines, resistor structures provided at points where the bitlines and the word lines cross each other and are located on the bitlines, and diode structures provided on the resistor structures incontact with the resistor structures and the word lines, lowerelectrodes provided on the substrate, resistor structures provided onthe lower electrodes, diode structures provided on the resistorstructures, and upper electrodes provided on the diode structures (see,e.g., patent document 3).

In such a configuration, since a unit cell structure is allowed to havea laminated-layer structure in which one diode structure and oneresistor structure are continuously laminated, an array cell structureis easily attainable.

A ReRAM having a cross-point configuration is also disclosed, in whichmemory plugs are arranged at cross points where X-direction conductivearray lines and Y-direction conductive array lines cross each other(e.g., see patent document 4). The memory plug is formed by sevenlayers. A composite metal oxide sandwiched between two electrode layersforms a memory element. A metal-insulator-metal (MIM) structure providedon the memory element forms a non-ohmic device.

The cross-point configuration is used for MRAM, or the like. Variousstudies have been made to solve the similar problems. For example, alaminated structure in which word lines, resistance variable layerpatterns, semiconductor layer patterns and bit lines are laminated, isdisclosed, in which the resistance variable layer pattern and thesemiconductor layer pattern form a schottky diode, or the semiconductorlayer pattern and the bit line form a schottky diode (see patentdocument 5).

Or, a MRAM including a plurality of word lines, a plurality of bitlines, and resistive intersection array of memory cells is disclosed, inwhich the memory cells are connected to bit lines and separate diodesand the separate diodes are connected to respective word lines (seee.g., patent document 6). The separate diode is formed as aschottky-metal-semiconductor diode, and its metal portion is suitablymade of platinum (Pt).

-   Patent document 1: Japanese Laid-Open Patent Application Publication    No. 2004-363604-   Patent Document 2: Japanese Laid-Open Patent Application Publication    No. 2003-68984-   Patent document 3: Japanese Laid-Open Patent Application Publication    No. 2006-140489-   Patent document 4: U.S. Pat. No. 6,753,561 specification-   Patent document 5: Japanese Laid-Open Patent Application Publication    No. 2003-197880-   Patent Document 6: Japanese Laid-Open Patent Application Publication    No. 2003-273335

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

The first example discloses a configuration including one diode having aswitching function and one resistor, but fails to disclose or suggest aspecific structure for the resistor and the diode. The second examplediscloses the cross-point configuration, but fails to disclose orsuggest series connection of the diode and its specific structure.

In contrast to these, the third example discloses a configuration inwhich the resistor structure is provided on the lower electrode, thediode structure is provided on the resistor structure, the upperelectrode is provided on the diode structure, and the diode structure isformed of a p-type oxide or an n-type oxide which are made of NiO, TiO₂,or the like. However, since the diode structure disclosed in the thirdexample has an outer dimension equal to that of the resistor structure,it is difficult to increase a current capacity of the diode structure.There is a problem that the diode having a small current capacity isincapable of conducting a sufficiently large current required forwriting and thereby stable operation of the ReRAM is not attained.

The fourth example has a problem that the resistance variable layer andthe non-ohmic device having the MIM structure are formed within thememory plug, and therefore, a manufacturing method is complex. Inaddition, in this configuration, since the non-ohmic device has the sameshape as the resistance variable layer, a current capacity of the diodecannot be increased. For this reason, the fourth example has a problemthat the stable operation of the ReRAM is not attained, as in the aboveexample.

The present invention is directed to solving the above describedproblems, and an object of the present invention is to provide anonvolatile semiconductor memory apparatus which is capable of securinga sufficiently large current capacity and of stable operation in across-point configuration including a non-ohmic device and a resistancevariable layer.

Means for Solving the Problem

With a view to achieving the above described object, a nonvolatilesemiconductor memory apparatus of the present invention comprises asubstrate; stripe-shaped lower-layer electrode wires provided on thesubstrate; an interlayer insulating layer which is disposed on thesubstrate including the lower-layer electrode wires and is provided withcontact holes at locations respectively opposite to the lower-layerelectrode wires; resistance variable layers which are respectivelyconnected to the lower-layer electrode wires; and non-ohmic deviceswhich are respectively provided on the resistance variable layers suchthat the non-ohmic devices are respectively connected to the resistancevariable layers; wherein the non-ohmic devices each has alaminated-layer structure including plural semiconductor layers, alaminated-layer structure including a metal electrode layer and aninsulator layer, or a laminated-layer structure including a metalelectrode layer and a semiconductor layer; and wherein one layer of thelaminated-layer structure is embedded to fill each of the contact holesand the semiconductor layer or the insulator layer which is the otherlayer of the laminated-layer structure has a larger area than an openingof each of the contact holes and is provided on the interlayerinsulating layer.

In such a configuration, a nonvolatile semiconductor memory apparatus isattainable, which is capable of simplifying the manufacturing step forthe non-ohmic devices, of lessening a variation in elementcharacteristics, of having high reproducibility and of providing asufficient current capacity.

In the above configuration, a plurality of constituent units, each ofwhich includes the interlayer insulating layer, the resistance variablelayer, and the non-ohmic device, are stacked to form a layer structure.

In such a configuration, a nonvolatile semiconductor memory apparatus isattainable, which is capable of lessening a variation in the property ofthe non-ohmic devices, of having high reproducibility, and of havingmemory portions with an extremely large capacity while ensuring asufficiently large current capacity.

In the above configuration, the other layers of the laminated-layerstructures respectively forming the non-ohmic devices may be provided instripe shape on the interlayer insulating layer so as to respectivelycross the lower-layer electrode wires. In such a configuration,pattering of the other layers of the laminated-layer structures isfacilitated. In addition, in the case where the metal electrode layer isused as the other layer, the metal electrode layer can serve as a partof the upper-layer electrode wire. Therefore, the manufacturing step canbe further simplified.

In the above configuration, the nonvolatile semiconductor memoryapparatus may further comprise stripe-shaped upper-layer electrode wireswhich are provided on the non-ohmic devices such that the upper-layerelectrode wires are respectively connected to the non-ohmic devices andrespectively cross the lower-layer electrode wires. In such aconfiguration, since the upper-layer electrode wires can be providedindependently of the non-ohmic devices, optimal materials can beselected for the upper-layer electrode wires and for the non-ohmicdevices. In addition, for example, when the resistance variable layersand the non-ohmic devices are formed on a silicon single crystalsubstrate provided with a semiconductor circuit including activeelements such as transistors, etc, electric connection between theupper-layer electrode wires and the active elements can be easily made.

In the above configuration, the non-ohmic devices may be MIM diodes eachhaving a laminated-layer structure including three layers which are aninsulator layer and metal electrode layers sandwiching the insulatorlayer, and the metal electrode layer which is closer to the resistancevariable layer may be embedded to fill each of the contact holes. Or,the non-ohmic devices may be MSM diodes each having a laminated-layerstructure including three layers which are a semiconductor layer andmetal electrode layers sandwiching the semiconductor layer, and themetal electrode layer which is closer to the resistance variable layermay be embedded to fill each of the contact holes.

In such a configuration, non-ohmic devices which have a large currentcapacity and have less variation in properties, are easily attainable.

In the above configuration, the non-ohmic devices may be p-n junctiondiodes each having a laminated-layer structure including two layerswhich are a p-type semiconductor layer and an n-type semiconductorlayer, and the p-type semiconductor layer or the n-type semiconductorlayer may be embedded to fill each of the contact holes. In such aconfiguration, crosstalk which would occur during reading or writing canbe further reduced by utilizing a rectifying property of the diodes. Inaddition, a circuit configuration therefor can be simplified.

In the above configuration, the non-ohmic devices may be schottky diodeseach having a laminated-layer structure including two layers which are asemiconductor layer and a metal electrode layer, and the metal electrodelayer may be embedded to fill each of the contact holes. In the schottkydiode having such a configuration, majority carrier is dominant.Therefore, a current capacity can be increased and a high-speedoperation can be achieved.

A method of manufacturing a nonvolatile semiconductor memory apparatusof the present invention comprises a step for forming stripe-shapedlower-layer electrode wires on a substrate; a step for forming aninterlayer insulating layer on the substrate including the lower-layerelectrode wires; a step for forming contact holes in an interlayerinsulating layer at locations respectively opposite to the lower-layerelectrode wires; a step for embedding resistance variable layers to fillthe contact holes except for portions at an upper side of the interlayerinsulating layer; a step for embedding at least one layers oflaminated-layer structures respectively forming non-ohmic devices tofill the portions at the upper side of the contact holes; and a step forforming, on the interlayer insulating layer, the other layers of thelaminated-layer structures respectively forming the non-ohmic devicessuch that the other layers have a larger area than openings of thecontact holes.

In such a method, since at least one layers of the laminated-layerstructures respectively forming the non-ohmic devices are embedded tofill the contact holes such that they are coplanar with the interlayerinsulating layer and have very smooth surfaces, a favorable interfacecondition of the non-ohmic devices is obtained. As a result, reductionor variation of the pressure resistance due to electric fieldconcentration or the like can be suppressed and a current capacity canbe increased.

In the above method, the step for embedding the resistance variablelayers to fill the contact holes may include a step for forming, insidethe contact holes and on the interlayer insulating layer, a firstdeposited film which is made of a material for the resistance variablelayers and a step for removing a portion of the first deposited filmwhich covers a surface of the interlayer insulating layer; and the stepfor embedding at least one layers of laminated-layer structuresrespectively forming non-ohmic devices to fill the portions at the upperside of the contact holes may include a step for removing portions ofthe first deposited film inside the contact holes to form recessesformed by the contact holes and the first deposited film, a step forforming, inside the recesses and on the interlayer insulating layer, asecond deposited film which is made of a material for the at least onelayers, and a step for removing a portion of the second deposited filmwhich covers the surface of the interlayer insulating layer.

In such a method, the resistance variable layer and the at least onelayers of the laminated-layer structure forming the non-ohmic device canbe respectively surely embedded to fill each of the contact holes.

The above method may further comprise repeating from the step forforming the interlayer insulating layer to the step for forming on theinterlayer insulating layer the other layers of the laminated-layerstructures respectively forming the non-ohmic devices plural times tostack the resistance variable layers and the non-ohmic devices to form alayer structure. In such a method, a nonvolatile semiconductor memoryapparatus including memory portions having a larger capacity isattainable.

In the above method, the other layers of the laminated-layer structuresrespectively forming the non-ohmic devices may be formed in stripe shapeon the interlayer insulating layer so as to respectively cross thelower-layer electrode wires. In such a method, pattering of the otherlayers of the laminated-layer structures is facilitated. In addition, inthe case where the metal electrode layer or the like is formed as theother layer, the metal electrode layer can serve as a part of theupper-layer electrode wire. Therefore, the manufacturing step can befurther simplified.

The above method may further comprise forming stripe-shaped upper-layerelectrode wires on the non-ohmic devices such that the upper-layerelectrode wires are respectively connected to the non-ohmic devices andrespectively cross the lower-layer electrode wires. Since theupper-layer electrode wires can be provided independently of thenon-ohmic devices, optimal materials can be selected for the upper-layerelectrode wires and for the non-ohmic devices and processes respectivelyadapted for them can be carried out. In addition, for example, whenusing a silicon single crystal substrate provided with a semiconductorcircuit including active elements such as transistors, etc, electricconnection between the upper-layer electrode wires and the activeelements can be easily made.

The above and further objects, features and advantages of the presentinvention will more fully be apparent from the following detaileddescription of preferred embodiments with accompanying drawings.

Effects of the Invention

The nonvolatile semiconductor memory apparatus of the present inventionhas great advantages that a current capacity is increased and a propertyof non-ohmic devices can be stabilized with simplified manufacturingsteps, since at least one layers respectively forming the non-ohmicdevices are embedded to fill the contact holes in the cross-pointconfiguration in which the non-ohmic devices are respectively connectedin series with the resistance variable layers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a plan view showing a configuration of a nonvolatilesemiconductor memory apparatus according to Embodiment 1 of the presentinvention. FIG. 1( b) is a cross-sectional view taken in the directionof arrows along line A-A.

FIG. 2( a) is a partially enlarged plan view showing a configuration ofmemory portions and non-ohmic devices which are a major part of anonvolatile semiconductor memory apparatus according to Embodiment 1.FIG. 2( b) is a cross-sectional view taken in the direction of arrowsalong line 2A-2A.

FIG. 3 is a block diagram schematically showing a circuit configurationof the nonvolatile semiconductor memory apparatus according toEmbodiment 1.

FIG. 4 is a view showing from the step for forming an interlayerinsulating layer on a substrate provided with active elements to thestep for forming contact holes in a manufacturing method of thenonvolatile semiconductor memory apparatus according to Embodiment 1.FIG. 4( a) is a cross-sectional view showing a state where theinterlayer insulating layer is formed. FIG. 4( b) is a plan view showinga state where contact holes are formed. FIG. 4( c) is a cross-sectionalview taken in the direction of arrows along line 3A-3A of FIG. 4( b).

FIG. 5 is a view showing a step for embedding resistance variable layersand embedded electrodes to fill the contact holes in the manufacturingmethod of the nonvolatile semiconductor memory apparatus according toEmbodiment 1. FIG. 5( a) is a cross-sectional view showing a state wherea thin-film resistance layer which becomes resistance variable layers isformed. FIG. 5( b) is a cross-sectional view showing a state where aportion of the thin-film resistance layer on the interlayer insulatinglayer is removed by CMP. FIG. 5( c) is a cross-sectional view showing astate where portions of the resistance variable layers inside thecontact holes are removed by over-polishing. FIG. 5( d) is across-sectional view showing a state where a thin-film electrode layerwhich becomes embedded electrodes is formed.

FIG. 6 is a view showing a state where resistance variable layers andembedded electrodes are embedded to fill the contact holes in themanufacturing method of the nonvolatile semiconductor memory apparatusaccording to Embodiment 1. FIG. 6( a) is a plan view. FIG. 6( b) is across-sectional view taken in the direction of arrows along line 4A-4Aof FIG. 6( b).

FIG. 7 is a view showing a state where insulator layers and upperelectrodes are formed in the manufacturing method of the nonvolatilesemiconductor memory apparatus according to Embodiment 1. FIG. 7( a) isa plan view. FIG. 7( b) is a cross-sectional view taken in the directionof arrows along line 4A-4A of FIG. 7( a).

FIG. 8 is a view showing a manufacturing method according toModification of the nonvolatile semiconductor memory apparatus accordingto Embodiment 1, showing a step for embedding resistance variable layersto fill the contact holes provided in the interlayer insulating layer.FIG. 8( a) is a cross-sectional view showing a state where the contactholes are formed. FIG. 8( b) is a cross-sectional view showing a statewhere a thin-film resistance layer which becomes the resistance variablelayers is formed. FIG. 8( c) is a cross-sectional view showing a statewhere a portion of the thin-film resistance layer on the interlayerinsulating layer is removed by CMP. FIG. 8( d) is a cross-sectional viewshowing a state where portions of the resistance variable layers insidethe contact holes are removed by over-polishing.

FIG. 9 is a view showing a manufacturing method of a nonvolatilesemiconductor memory apparatus according to Modification of Embodiment1, showing from the step for embedding the resistance variable layersand the embedded electrodes to fill the contact holes to the step forforming grooves for embedding the insulator layers and the upperelectrodes in the interlayer insulating layer. FIG. 9( a) is a viewshowing a state where a thin-film electrode layer which becomes theembedded electrodes is formed. FIG. 9( b) is a cross-sectional viewshowing a state where a portion of the thin-film electrode layer on theinterlayer insulating layer is removed by CMP. FIG. 9( c) is across-sectional view showing a state where the interlayer insulatinglayer is formed. FIG. 9( d) is a cross-sectional view showing a statewhere grooves are formed in the interlayer insulating layer.

FIG. 10 is a view showing a manufacturing method according toModification of the nonvolatile semiconductor memory apparatus accordingto Embodiment 1, showing a step for embedding the insulator layers andthe upper electrodes to fill the grooves. FIG. 10( a) is across-sectional view showing a state where a thin-film insulating layerwhich becomes the insulator layers and the thin-film electrode layerwhich becomes the upper electrodes are formed on the interlayerinsulating layer including the grooves. FIG. 10( b) is a cross-sectionalview showing a state where portions of the thin-film electrode layer andthe thin-film insulating layer on the interlayer insulating layer areremoved by CMP, embedding portions thereof to fill the grooves.

FIG. 11 is a cross-sectional view showing a configuration of anonvolatile semiconductor memory apparatus according to Embodiment 2 ofthe present invention.

FIG. 12 is a cross-sectional view showing a configuration of memoryportions and non-ohmic devices which are major constituents of anonvolatile semiconductor memory apparatus according to Embodiment 3 ofthe present invention.

FIG. 13 is a cross-sectional view showing a configuration of memoryportions and non-ohmic devices which are major constituents of anonvolatile semiconductor memory apparatus according to Embodiment 4 ofthe present invention.

FIG. 14 is a cross-sectional view showing a configuration of memoryportions and non-ohmic devices which are major constituents of anonvolatile semiconductor memory apparatus according to Embodiment 5 ofthe present invention. FIG. 14( a) is a plan view. FIG. 14( b) is across-sectional view taken in the direction of arrows along line14A-14A.

DESCRIPTION OF REFERENCE NUMERALS

5 word line decoder

6 bit line decoder

7 readout circuit

10, 40, 70, 90, 100 nonvolatile semiconductor memory apparatus (ReRAM)

11 substrate

12 active element

12 a source region

12 b drain region

12 c gate insulating film

12 d gate electrode

13, 14 semiconductor interlayer insulating layer

15, 15 a, 71, 91, 91 a, 101, 101 a lower-layer electrode wire

16, 30, 31, 92, 109 interlayer insulating layer

17 memory portion (first memory portion)

18, 76, 94, 104 resistance variable layer

19, 79, 95, 105 embedded electrode (metal electrode layer)

20 non-ohmic device (first non-ohmic device)

21, 34, 107 insulator layer

22, 35, 81, 99, 108 upper electrode

23 insulating protecting layer (first interlayer insulating layer)

24, 25, 28, 50, 51 embedded conductor

26 semiconductor electrode wire

27, 27 a upper-layer electrode wire (first upper-layer electrode wire)

29 contact hole

30 a first insulating layer

30 b second insulating layer

32 groove

41 second memory portion (memory portion)

42 second resistance variable layer

43 second embedded electrode

44 second non-ohmic device (non-ohmic device)

45 second insulator layer

46 second upper electrode

47 second interlayer insulating layer

48 third interlayer insulating layer

49, 49 a second upper-layer electrode wire

52 fourth interlayer insulating layer

53 third memory portion (memory portion)

54 third resistance variable layer

55 third embedded electrode

56 third non-ohmic device (non-ohmic device)

57 third insulator layer

58 third upper electrode

59 third upper-layer electrode wire

60 insulating protective layer

75 memory portion

72 lower wire

73, 73 a, 77, 82 connection electrode

75, 93, 103 memory portion

78, 96, 106 non-ohmic device

80 semiconductor layer

97 p-type semiconductor layer

98 n-type semiconductor layer

110 upper-layer electrode wire

181 thin-film resistance layer

191, 351 thin-film electrode layer

341 thin-film insulating layer

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the drawings.

Hereinafter, embodiments of the present invention will be described withreference to the drawings. The same components or constituents areidentified by the same reference numbers and will not be describedrepetitively in some cases. In addition, the shapes of transistors,memory portions and others are schematically shown and the numbers ofthem are set for easier illustration.

(Embodiment 1)

FIG. 1 is a view showing a configuration of a nonvolatile semiconductormemory apparatus 10 according to Embodiment I of the present invention.FIG. 1( a) is a plan view. FIG. 1( b) is a cross-sectional view taken inthe direction of arrows along line 1A-1A. In the plan view of FIG. 1(a), a part of an insulating protective film corresponding to anuppermost layer is illustrated as being cut away for easierunderstanding. FIG. 2 is a partially enlarged plan view of a major partof memory portions 17 and non-ohmic devices 20. FIG. 2( a) is a planview. FIG. 2( b) is a cross-sectional view taken in the direction ofarrows along line 2A-2A.

The nonvolatile semiconductor memory apparatus 10 of this embodimentcomprises a substrate 11, stripe-shaped lower-layer electrode wires 15provided on the substrate 11, an interlayer insulating layer 16 which isprovided on the substrate 11 including the lower-layer electrode wires15 and provided with contact holes at locations respectively opposite tothe lower-layer electrode wires 15, resistance variable layers 18 whichare respectively embedded to fill the contact holes and are respectivelyconnected to the lower-layer electrode wires 15, and non-ohmic devices20 are provided on the resistance variable layers 18 such that thenon-ohmic devices 20 are respectively connected to the resistancevariable layers 18.

In this embodiment, the non-ohmic device 20 is a MIM diode which has alaminated structure including three layers which are an embeddedelectrode 19 which is a metal electrode layer, an upper electrode, 22,and an insulator layer 21. One layer of the laminated structure, i.e.,the embedded electrode 19 which is the metal electrode layer is embeddedto fill the contact hole. The other layers of the laminated structure,i.e., the insulator layer 21 and the upper electrode 22 have a largershape (area) than the opening of the contact hole and are provided onthe interlayer insulating layer 16.

Furthermore, in this embodiment, the insulator layers 21 and the upperelectrodes 22 are provided in strip-shape on the interlayer insulatinglayer so as to respectively cross the lower-layer electrode wires 15.Each upper electrode 22 forms a part of an upper-layer electrode wire.Memory portions 17 are each constituted by the resistance variable layer18, a lower-layer electrode wire 15 a connected to the resistancevariable layer 18 and the embedded electrode 19 connected to theresistance variable layer 18. As the resistance variable layer 18, anoxide containing iron, for example, triiron tetroxide (Fe₃O₄) isdesirably used to stabilize the resistance varying characteristics,obtain reproducibility in manufacturing, etc. The MIM diode which is thenon-ohmic 20 is formed by a laminated structure of three layers whichare the embedded electrode 19, the insulator layer 21, and the upperelectrode 22. As shown in FIG. 1, the insulator layers 21 and the upperelectrodes 22 are extended to outside the region where the memoryportions 17 and the non-ohmic devices 20 are arranged in matrix. Theupper electrodes 22 are connected to the upper-layer electrode wires 27outside the matrix region. Within the matrix region, the upperelectrodes 22 also serve as the upper-layer electrode wires.

In this embodiment, there is provided a semiconductor circuit in whichactive elements 12 such as transistors are integrated on a siliconesingle crystal substrate used as the substrate 11. Whereas thetransistors each including the source region 12 a, the drain region 12b, the gate insulating film 12 c and the gate electrode 12 d are shownas the active elements 12, elements generally required for the memorycircuit such as DRAM are provided in addition to the active elements 12.

The lower-layer electrode wires 15 and the upper-layer electrode wires27 are connected to the active elements 12 in regions different from thematrix region where the memory portions 17 and the non-ohmic devices 20are arranged. To be specific, as shown in FIG. 1, the lower-layerelectrode wire 15 is connected to the source region 12 a of the activeelement 12 via the embedded conductors 24 and 25, and the semiconductorelectrode wire 26. The upper-layer electrode wire 27 is connected toanother active element (not shown) via the embedded conductor 28 in thesame manner.

The lower-layer electrode wire 15 is formed by sputtering using, forexample, Ti—Al—N alloy, Cu or Al and is easily formed by an exposureprocess and an etching process. The resistance variable layer 18 formingthe memory portion 17 may be formed by sputtering or the like using atransition metal oxide such as a titanium oxide, a vanadium oxide, acobalt oxide, a nickel oxide, a zinc oxide, or a niobium oxide, as wellas a triiron tetroxide which is the iron oxide. Such a transition metaloxide material is allowed to have a specific resistance value when it isapplied with a voltage or current having a threshold or higher andmaintains the resistance value until it is newly applied with a pulsevoltage or pulse current having a constant magnitude.

As the interlayer insulating layer 16, an insulating oxide material maybe used. To be specific, a silicon oxide (SiO) deposited by the CVDprocess, TEOS-SiO layer deposited by the CVD process using ozone (O₃)and tetraethoxysilane (TEOS), or silicon nitride (SiN) layer may beused. Alternatively, silicon carbon nitride (SiCN) or silicon oxycarbite(SiOC) which is a low-dielectric constant material, or fluorine-dopedsilicon oxide (SiOF) may be used.

As the non-ohmic device 20, a MIM diode having a laminated structure inwhich the embedded electrode 19 and the upper electrode 22 made of, forexample, tantalum (Ta), aluminum (Al) or a combination of these and theinsulator layer 21 made of silicon nitride (SiN) may be used. As theelectrode, Ti or Cr may be used, in addition to Al. If they are used,the wire resistance increases. Therefore, a laminated structure of thinfilms made of Al or Cu is desirably used.

FIG. 3 is a block diagram showing a schematic circuit configuration ofthe nonvolatile semiconductor memory apparatus 10 of this embodiment. Asshown in FIG. 1, the memory portion 17 is connected in series with thenon-ohmic device 20, one end of the memory portion 17 is connected tothe lower-layer electrode wire 15, and one end of the non-ohmic device20 is connected to the upper-layer electrode wire 27. The lower-layerelectrode wire 15 is connected to a bit line decider 6 and to a readoutcircuit 7. The upper-layer electrode wire 27 is connected to a word linedecoder 5. Thus, the lower-layer electrode wires 15 serve as bit linesand the upper-layer electrode wires 27 serve as word lines. Thelower-layer electrode wires 15 and the upper-layer electrode wires 27are arranged in matrix. The bit line decoder 6, the word line decoder 5,and the readout circuit 7 form peripheral circuits. The peripheralcircuits include the active elements 12 constituted by, for example,MOSFET.

Subsequently, a manufacturing method of the nonvolatile semiconductormemory apparatus 10 of this embodiment will be described with referenceto FIGS. 4 to 7.

FIG. 4 is a view showing from the step for forming constituents and theinterlayer insulating layer 16 on the substrate 11 provided with activeelements 12 to the step for forming contact holes 29. FIG. 4( a) is across-sectional view showing a state where the interlayer insulatinglayer 16 is formed. FIG. 4( b) is a plan view showing a state wherecontact holes 29 are formed. FIG. 4( c) is a cross-sectional view takenin the direction of arrows along line 4A-4A of FIG. 4( b). Thecross-sections shown in FIGS. 5 to 10 are taken along line 4A-4A,including the cross-section of FIG. 4( a).

FIG. 5 is a view showing a step for embedding resistance variable layers18 and embedded electrodes 19 to fill the contact holes 29. FIG. 5( a)is a cross-sectional view showing a state where a thin-film resistancelayer 181 which becomes the resistance variable layers is formed. FIG.5( b) is a cross-sectional view showing a state where a portion of thethin-film resistance layer 181 on the interlayer insulating layer 16 isremoved by CMP. FIG. 5( c) is a cross-sectional view showing a statewhere portions of the resistance variable layers 18 inside the contactholes 29 are removed by over-polishing. FIG. 5( d) is a cross-sectionalview showing a state where a thin-film electrode layer 191 which becomesembedded electrodes 19 is formed.

FIG. 6 is a view showing a state where the resistance variable layers 18and the embedded electrodes 19 are embedded to fill the contact holes29. FIG. 6( a) is a plan view. FIG. 6( b) is a cross-sectional viewtaken in the direction of arrows along line 4A-4A.

FIG. 7 is a view showing a state where the insulator layers 21 and theupper electrodes 22 are formed. FIG. 7( a) is a plan view and FIG. 7( b)is a cross-sectional view.

Initially, as shown in FIG. 4( a), on the substrate 11 provided with aplurality of active elements 12, semiconductor electrode wires 26 andsemiconductor interlayer insulating layers 13 and 14, the lower-layerelectrode wires 15 and the interlayer insulating layer 16 are formed.Aluminum was usually used for the semiconductor electrode wires 26, butin recent years, cupper which attains low-resistance state even in aminiaturized structure is primarily used. For the semiconductorinterlayer insulating layers 13 and 14, a fluorine-containing oxide(e.g., SiOF), a carbon-containing nitride (e.g., SiCN) or an organicresin material (e.g., polyimide) is used to reduce a parasiticcapacitance between the wires. In this embodiment, for the semiconductorelectrode wires 26, for example, cupper may be used, and for thesemiconductor interlayer insulating layers 13 and 14, for example, afluorine-containing oxide SiOF my be used.

The lower-layer electrode wires 15 are embedded in the semiconductorinterlayer insulating layer 14. They are formed in a manner describedbelow. To be specific, stripe-shaped grooves for embedding thelower-layer electrode wires 15 and contact holes connected with thesemiconductor electrode wires 26 are formed in the semiconductorinsulating layer 14. They can be easily formed using a technique used ina general semiconductor process. After the grooves and the contact holesare formed, the electric conductor film which becomes the lower-layerelectrode wires 15 is formed. Then, by conducting, for example, CMP, thelower-layer electrode wires 15 having the shape shown in FIG. 4( a) areformed. As the lower-layer electrode wires 15, for example, Cu, Al,Ti—Al alloy or a laminated structure of these may be used, other thanabove described Ti—Al—N alloy.

Then, as shown in FIG. 4( a), on the substrate 11 including thelower-layer electrode wires 15, the interlayer insulting layer 16 madeof TEOS-SiO is deposited using, for example, the CVD process. For theinterlayer insulating layer 16, various materials may be used asdescribed above.

Then, as shown in FIGS. 4( b) and 4(c), the contact holes 29 are formedat constant arrangement pitches in the interlayer insulating layer 16 onthe lower-layer electrode wires 15. The contact holes 29 have an outershape which is smaller than the width of the lower-layer electrode wires15, as can be seen from FIG. 4( b). The contact holes 29 have aquadrangular shape as shown in FIG. 4, but may be a circular shape, anoval shape, or other shape. The contact holes 29 are formed by a generalsemiconductor process, and detail explanation thereof is omitted.

Then, as shown in FIG. 5( a), on the interlayer insulating layer 16including the contact holes 29, a thin-film resistance layer 181 (firstdeposited film) which becomes the resistance variable layers 18 isformed. In this embodiment, the thin-film resistance layer 181 is formedin such a manner that Fe₃O₄ which is the material for the resistancevariable layers 18 is deposited into the contact holes 29 and on theinterlayer insulating layer 16 by the sputtering process. As the filmforming method, the CVD process or an ALD process may be used, insteadof the sputtering process.

Then, as shown in FIG. 5( b), only a portion of the thin-film resistancelayer 181 which covers the surface of the interlayer insulating layer 16is removed using the CMP process, embedding the resistance variablelayers 18 to fill the contact holes 29.

Then, as shown in FIG. 5( c), by further conducting the over-polishing,portions of the resistance variable layers 18 inside the contact holes29 are removed. As a result, as shown in FIG. 5( c), recesses are formedby the contact holes 29 and the resistance variable layers 18 (remainingportions of the first deposited film). Using the over-polishingtechnique of the CMP, the portions of the resistance variable layers 18can be removed to a depth (recess depth) of the contact holes 29 intowhich a polishing pad of the CMP intrudes. The use of the over-polishingtechnique of the CMP favorably facilitates the depth control for therecesses.

As the method of removing the portions of the resistance variable layers18, the resistance variable layers 18 may be etched back instead of theover-polishing.

Then, as shown in FIG. 5( d), a thin-film electrode layer 191 (seconddeposited film) which becomes the embedded electrodes 19 is formed onthe interlayer insulating layer 16 including the contact holes 29(recesses). In this embodiment, the thin-film electrode layer 191becomes a part of the memory portions 17 and a part of the non-ohmicdevices 20. As the material for the thin-film electrode layer 191, Alwhich is the material for a part of the memory portions 17 and a part ofthe ohmic devices 20 was used. The AL material for the thin-filmelectrode layer 191 is deposited inside the recesses and on theinterlayer insulating layer 16 as shown in FIG. 5( d).

Then, as shown in FIG. 6, only a portion of the thin-film electrodelayer 191 covering the surface of the interlayer insulating layer 16 isremoved by using the CMP process, embedding the embedded electrodes 19to fill the contact holes 29.

Then, as shown in FIG. 7, the insulator layers 21 and the upperelectrodes 22 are deposited such that they are connected to the embeddedelectrodes 19. In this case, the insulator layers 21 and the upperelectrodes 22 are formed in stripe shape on the interlayer insulatinglayer 16 such that the insulator layers 21 and the upper electrodes 22have a larger shape (area) than at least the openings of the contactholes 29 and respectively cross the lower-layer electrode wires 15. Inthis embodiment, aluminum (Al) was used for the embedded electrodes 19and the upper electrodes 22, and SiN was used for the insulator layers21. SiN is easily formed by the sputtering process to make a thin filmwhich is favorable in insulation property and highly dense. A current(I) flowing in the MIM diode which is the non-ohmic device 20 formed inthis way is derived from the formula (1). The following formula (1) isestablished even when using a metal-semiconductor-metal (MSM) diode asdescribed later (Embodiment 3). Herein, the detail description for thecase of using the MSM diode will be omitted.I=S·α·V·exp(β·√V)  (1)herein, α=(n·μ·q·d)exp(−E/kT)β=(1/kT)·√(q ³/(x·ε ₀·ε_(opt) ·d))

In the formula (1), S is the area of the MIM diode (or area of MSMdiode), n is a carrier density, μ is a mobility, q is an electric chargeof electrons, d is the thickness of the insulator layer (thickness ofthe semiconductor layer in the case of the MSM diode), E is a trapdepth, k is a Boltzmann constant, T is an absolute temperature, ε₀ isthe permittivity of vacuum, ε_(opt) is an optical dielectric constant ofthe insulator layer (semiconductor layer in the case of the MSM diode).

As should be understood from the formula (1), the current flowing in theMIM diode is proportional to the area of the MIM diode. Also, thecurrent is more difficult to flow as the thickness of the insulatorlayer 21 increases. Accordingly, in order to obtain a large currentcapacity with a low voltage, the insulator layer 21 is required to bethinned. However, in the conventional structure for embedding the entireof the resistance variable layer and the entire of the non-ohmic deviceto fill the contact hole, pressure resistance of the insulator layer 21may in some cases reduce if the insulator layer 21 is thinned.

It is considered that, in the conventional manufacturing method of theMIM diode (see e.g., U.S. Pat. Nos. 6,034,882 and U.S. Pat. No.7,265,000), if the insulator layer 21 is formed to be thinner, the upperand lower electrodes of the MIM diode tend to contact each other due toadhesion of the electrode material in an outer peripheral region of theinsulator layer in the process for manufacturing the MIM diode andtherefore, leak tends to occur. That is, according to thesepublications, the memory plugs containing the MIM diodes aremanufactured by entirely removing the multi-layer film formed in a solidstate using a suitable mask. Therefore, there is a likelihood that theupper and lower electrodes of the MIM diode electrically contact eachother due to adhesion of the electrode material removed from themulti-layer film to the MIM diode, if the insulator layer 21 is formedto be thinner in the conventional manufacturing method of the MIM diode.

In contrast, in this embodiment, as shown in FIG. 6, the embeddedelectrodes 19 are entirely embedded to fill the contact holes 29, andthe surfaces thereof are smoothed to a great degree by conducting theCMP. When the insulator layers 21 are formed on the flattened surfaces,they are dense and continuous even if the thickness of them is smaller.Therefore, the pressure resistance of the insulator layers 21 can besecured properly even if the insulator layers 21 are formed to bethinner. In addition, since the embedded electrodes 19 are entirelycovered with the insulator layers 21, an event that the embeddedelectrode 19 and the upper electrode 22 contact and leak occurs in theouter peripheral region of the insulator layer 21 does not take place.Furthermore, since the upper electrode 22 is provided to extend to asurrounding region of the embedded electrode 19, the current pulseflowing in the non-ohmic device is formed to spread to outside the areaof the embedded electrode. In this case, since an electric force linebased on an electric field spreads in the direction from the embeddedelectrode 19 inside the contact hole 29 to the insulator layer 21, aneffective area of the MIM diode is larger than the area of theconventional MIM diode whose layers are all filled in the contact hole.Therefore, the non-ohmic device 20 which has a larger current capacityand less variation in properties than the conventional element isattainable.

The upper-layer electrode wires 27 are connected to the upper electrodes22 outside the region where the memory portions 17 and the MIM diodeswhich are the non-ohmic devices 20 are arranged in matrix. For theupper-layer electrode wires 27, the material similar to that for thelower-layer electrode wires 15 may be used. The embedded conductors 28are formed at the same time that the upper-layer electrode wires 27 areformed. The upper-layer electrode wires 27 are connected to thesemiconductor electrode wires (not shown) via the embedded conductors 28and electrically connected to the active elements provided at locationswhich are not shown.

Thereafter, the insulating protective layer 23 is formed to cover theupper electrodes 22 and the upper-layer electrode wires 27, therebymanufacturing the nonvolatile semiconductor memory apparatus 10 as shownin FIG. 1.

Having described an example in which the MIM diode includes SiN as theinsulator layer 21 in this embodiment, the present invention is notlimited to this. For example, tantalum oxide (TaO), alumina (AlO), ortitania (TiO) may be used. In the case of using TaO, TaO may be formedin any method. For example, TaO may be formed by a dry heat oxidationprocess, a wet heat oxidation process, or a plasma oxidation processafter a Ta film is formed, or otherwise TaOx film may be directly formedby a reactive sputtering process, etc.

Subsequently, a manufacturing method of modification of this embodimentwill be described with reference to FIGS. 8 to 10. As shown in FIGS. 8to 10, only the interlayer insulating layer 14 and constituents locatedthereabove are illustrated for the sake of simplified illustration.

FIG. 8 is a view showing steps for embedding resistance variable layersto fill the contact holes 29 provided in the interlayer insulating layer30. FIG. 8( a) is a cross-sectional view showing a state where thecontact holes 29 are formed. FIG. 8( b) is a cross-sectional viewshowing a state where a thin-film resistance layer 181 which becomes theresistance variable layers 18 is formed. FIG. 8( c) is a cross-sectionalview showing a state where a portion of the thin-film resistance layer181 on the interlayer insulating layer 30 is removed. FIG. 8( d) is across-sectional view showing a state where portions of the resistancevariable layers 18 inside the contact holes 29 are further removed byover-polishing.

FIG. 9 is a view showing from the step for embedding the resistancevariable layers 18 and the embedded electrodes 19 to fill the contactholes 29 to the step for forming grooves 32 for embedding insulatorlayers 34 and the upper electrodes 35 in the interlayer insulating layer31. FIG. 9( a) is a view showing a state where a thin-film electrodelayer 191 which becomes the embedded electrode layers 19 is formed. FIG.9( b) is a cross-sectional view showing a state where a portion of thethin-film electrode layer 191 on an interlayer insulating layer 30 isremoved by the CMP. FIG. 9( c) is a cross-sectional view showing a statewhere an interlayer insulating layer 31 is formed. FIG. 9( d) is across-sectional view showing a state where the grooves 32 are formed inthe interlayer insulating layer 31.

FIG. 10 is a view showing a step for embedding the insulator layers 34and the upper electrodes 35 to fill the grooves 32. FIG. 10( a) is across-sectional view showing a state where a thin-film insulating layer341 which becomes the insulator layers 34 and a thin-film electrodelayer 351 which becomes the upper electrodes 35 are formed on theinterlayer insulating layer 31 including the grooves 32. FIG. 10( b) isa cross-sectional view showing a state where portions of the thin-filmelectrode layer 351 and the thin-film insulating layer 341 on theinterlayer insulating layer 31 are removed and portions thereof areembedded to fill the grooves 32.

Initially, as shown in FIG. 8( a), on the substrate (not shown)including the lower-layer electrode wires 15, a first insulating layer30 a made of TEOS-SiO and a second insulating layer 30 b made of, forexample, SiON which is harder than TEOS-SiO, are deposited, using, forexample, the CVD process. The first insulating layer 30 a and the secondinsulating layer 30 b form the interlayer insulating layer 30. Thesecond insulating layer 30 b serves as a stopper in the CMP process. Byforming the second insulating layers 30 b, the CMP process is easily andsurely conducted. Then, the contact holes 29 are formed at constantarrangement pitches in the interlayer insulating layer 30 on thelower-layer electrode wires 15. The contact holes 29 have an outer shapesmaller than the width of the lower-layer electrode wires 15, and areformed as in the manufacturing steps shown in FIGS. 4 to 7 and to have ashape as shown in FIGS. 4 to 7.

Then, as shown in FIG. 8( b), on the interlayer insulating layer 30including the contact holes 29, the thin-film resistance layer 181(first deposited film)which becomes the resistance variable layers 18 isformed. In this embodiment, as the resistance variable layers 18, Fe₃O₄was deposited by the sputtering process. As the film forming method, theCVD process or the ALD process may be used, instead of the sputtering.

Then, as shown in FIG. 8( c), using the CMP process, a portion of thethin-film resistance layer 181 on the interlayer insulating layer 30 isremoved, embedding resistance variable layers 18 to fill the contactholes 29. In this case, since the second insulating layer 30 b includedin the interlayer insulating layer 30 effectively serves as the stopper,only the thin-film resistance layer 181 can be surely removed withoutsubstantially polishing the interlayer insulating layer 30.

Then, as shown in FIG. 8( d), by conducting over-polishing, portions ofthe resistance variable layers 18 inside the contact holes 18 areremoved. During the over-polishing, the interlayer insulating layer 30is not subjected to polishing because of the presence of the secondinsulating layer 30 b. Alternatively, the portions of the resistancevariable layers 18 may be removed by etch back instead of theover-polishing.

Then, as shown in FIG. 9( a), on the interlayer insulating layer 30including the contact holes 29, the thin-film electrode layer 191(second deposited film) which becomes the embedded electrodes 19 isformed. The thin-film electrode layer 191 becomes a part of the memoryportions 17 and a part of the non-ohmic devices 20 and is made of Al.

Then, as shown in FIG. 9( b), a portion of the thin-film electrode layer191 on the interlayer insulating layer 30 is removed by the CMP process,embedding embedded electrodes 19 to fill the contact holes 29. In thiscase, also, since the second insulating layer 30 b included in theinterlayer insulating layer 30 effectively serves as the stopper, onlythe thin-film electrode layer 191 can be surely removed withoutsubstantially polishing the interlayer insulating layer 30.

Then, as shown in FIG. 9( c), on the interlayer insulating layer 30including the embedded electrodes 19, the interlayer insulating layer 31is further formed. The interlayer insulating layer 31 is formed to havea thickness required to embed the insulator layers 34 and the upperelectrodes 35. As a material for the interlayer insulating layer 3,TEOS-SiO may be used. Alternatively, other interlayer insulatingmaterials which are generally used in the semiconductor apparatuses maybe used for the interlayer insulating layer 31. Furthermore, as in theinterlayer insulating layer 30, the interlayer insulating layer 31 mayhave a double-layer structure including a hard insulating layer formedas the upper layer.

Then, as shown in FIG. 9( d), stripe-shaped grooves 32 are formed suchthat the embedded electrodes 19 are exposed and the grooves 32respectively cross the lower-layer electrode wires 15. The process canbe carried out using a general semiconductor process, for example, dryetching.

Then, as shown in FIG. 10( a), on the interlayer insulating layer 31including the grooves 32, the thin-film insulating later 341 whichbecomes the insulator layers 34 and the thin-film electrode layer 351which becomes the upper electrodes 35 are formed. As the materials forthe thin-film insulating layer 341 and the thin-film electrode layer351, the materials described in this embodiment may be used.

Then, as shown in FIG. 10( b), portions of the thin-film electrode layer351 and the thin-film insulator layer 341 on the interlayer insulatinglayer 31 are removed by the CMP process, embedding the insulator layers34 and the upper electrodes 35 to fill the grooves 32. Through thisstep, the memory portions 17 are each formed to include the resistancevariable layer 18, and the lower-layer electrode wire 15 a and theembedded electrode 19 sandwiching the resistance variable layer 18,while the non-ohmic devices 33 are each formed to include the embeddedelectrode 19, the insulator layer 34 and the upper electrode 35.Further, thereafter, the insulating protective layer (not shown) forprotecting the upper electrodes is formed. In this manner, thenonvolatile semiconductor memory apparatus according to themanufacturing method of modification of this embodiment is manufactured.

In the nonvolatile semiconductor memory apparatus manufactured by theabove described manufacturing method, the insulator layers 34 and theupper electrodes 35 are embedded in the interlayer insulating layer 31.Therefore, in the case where the memory portions 17 and the non-ohmicdevices 33 are further laminated, the laminating steps therefor areeasily carried out.

In the nonvolatile semiconductor memory apparatus of this modification,as shown in FIG. 10( b), the insulator layer 34 having a substantiallyU-shaped cross section is provided to cover the lower surface and bothside surfaces of each upper electrode 35. For this reason, there is anadvantage that the insulator layer 34 can serve as a barrier filmdepending on the selection of the insulating material for the interlayerinsulating layer 31 or the metal material for the upper electrode 35.

(Embodiment 2)

FIG. 11 is a cross-sectional view showing a configuration of anonvolatile semiconductor memory apparatus 40 according to Embodiment 2of the present invention. The nonvolatile semiconductor memory apparatus40 has a configuration in which on a base structure which is thenonvolatile semiconductor memory apparatus 10 of Embodiment 1 shown inFIG. 1, two layers of a constituent unit including the interlayerinsulating layer, the resistance variable layers and the non-ohmicdevices which are embedded to fill the contact holes formed in theinterlayer insulating layer, are stacked on the base structure to form alayered structure. Such a layered structure can attain a nonvolatilesemiconductor memory apparatus with a larger capacity.

Hereinafter, the configuration of the nonvolatile semiconductor memoryapparatus 40 of this embodiment will be described. In the nonvolatilesemiconductor memory apparatus 10 shown in FIG. 1, the insulator layers21 and the upper electrodes 22 are connected to the upper-layerelectrode wires 27 outside the region where the memory portions 17 andthe non-ohmic devices 20 are arranged in matrix. On the other hand, inthe nonvolatile semiconductor memory apparatus 40 of this embodiment,the upper-layer electrode wires 27 are extended to a region above theupper electrodes 22 within the matrix region, which occurs also in thesecond and third stages. In the nonvolatile semiconductor memoryapparatus 40, the memory portions and the non-ohmic devices arerespectively stacked in three stages. To easily understand theconstituents in the first, second, and third stages, the constituents inthe first stage are expressed as first constituents, the constituents inthe second stage are expressed as second constituents, and theconstituents in the third stage are expressed as third constituents.

On the first interlayer insulating layer 23 including the firstupper-layer electrode wires 27, a second interlayer insulating layer 47is further provided. The second interlayer insulating layer 47 isprovided with contact holes at locations respectively corresponding tothe first memory portions 17. Second resistance variable layers 42 andsecond embedded electrodes 43 are embedded to fill the contact holes.Second insulator layers 45, second upper electrodes 46, and secondupper-layer electrode wires 49 are provided in stripe shape such thatthey are respectively connected to the second embedded electrodes 43 andrespectively cross the first upper-layer electrode wires 27. Further, athird interlayer insulating layer 48 is provided so that theseconstituents are embedded therein.

On the second upper-layer electrode wires 49 and the third interlayerinsulating layer 48, a fourth interlayer insulating layer 52 isprovided. The fourth interlayer insulating layer 52 is provided withcontact holes at locations respectively corresponding to the firstmemory portions 17 and the second memory portions 41. Third resistancevariable layers 54 and third embedded electrodes 55 are embedded to fillthe contact holes. Third insulator layers 57, third upper electrodes 58,and third upper-layer electrode wires 59 are provided in stripe shapesuch that they are respectively connected to the third embeddedelectrodes 55 and respectively cross the second upper-layer electrodewires 49. Further, an insulating protecting layer 60 is provided so thatthese constituents are embedded therein and protected.

The second memory portions 41 are each constituted by the secondresistance variable layer 42, a first upper-layer electrode wire 27 aand the second embedded electrode 43 sandwiching the second resistancevariable layer 42. The second non-ohmic devices 44 are each constitutedby the second embedded electrode 43, the second insulator layer 45 andthe second upper electrode 46. The third memory portions 53 are eachconstituted by the third resistance variable layer 54, a secondupper-layer electrode wire 49 a and the embedded electrode 55sandwiching the third resistance variable layer 54. The third non-ohmicdevices 56 are each constituted by the third embedded electrode 55, thethird insulator layer 57 and the third upper electrode 58.

The lower-layer electrode wire 15 is connected to the source region 12 aof the active elements 12 via the embedded conductors 24 and 25, and thesemiconductor electrode wire 26. In the same manner, the firstupper-layer electrode wire 27 is connected to another active element(not shown) via the embedded conductor (not shown) and the semiconductorelectrode wire (not shown). As shown in FIG. 11, the second upper-layerelectrode wire 49 is connected to the source region 12 a of anotheractive element 12 via the embedded conductors 24, 25, 50, and 51 and thesemiconductor electrode wire 26. The third upper-layer electrode wire 59is connected to another active element (not shown) via the embeddedconductor (not shown) and the semiconductor electrode wire (not shown),as in the first upper-layer electrode wire 27.

The lower-layer electrode wires 15 and the first upper-layer electrodewires 27 in the first stage serve as bit lines or word lines and areconnected to the bit line decoder or the word line decoder in thecircuit shown in FIG. 3. Also, in the same manner, the first upper-layerelectrode wires 27 and the second upper-layer electrode wires 49 serveas bit lines or word lines and are connected to the bit line decoder orthe word line decoder in the circuit shown in FIG. 3. The nonvolatilesemiconductor memory apparatus 40 is designed so that when the firstupper-layer electrode wires 27 serve as the bit lines in the firststage, they serve as the bit lines in the second stage as well, and thesecond upper-layer electrode wires 49 serve as the word lines. Thenonvolatile semiconductor memory apparatus 40 is designed so that whenthe second upper-layer electrode wires 49 serve as the word lines, thethird upper-layer electrode wires 59 serve as the bit lines.

As described above, in the nonvolatile semiconductor memory apparatus40, the non-ohmic devices 20, 44, and 56 are respectively provided forthe memory portions 17, 41, and 53 in the respective stages, writing andreading are stably and surely performed for the memory portions 17, 33,and 45 provided in the respective stages.

The manufacturing steps for the nonvolatile semiconductor memoryapparatus 40 having the memory portions and the non-ohmic devices in theabove multi-stage configuration may be accomplished basically byrepeating the two kinds of manufacturing steps described for thenonvolatile semiconductor memory apparatus 40 of Embodiment 1

(Embodiment 3)

FIG. 12 is a cross-sectional view showing a configuration of memoryportions 75 and non-ohmic devices 78 which are major constituents of anonvolatile semiconductor memory apparatus 70 according to Embodiment 3of the present invention. In the nonvolatile semiconductor memoryapparatus 70 of this embodiment, a lower-layer electrode wire 71includes at least two layers, and at the side connected with theresistance variable layer 76, an electrically conductor material whichmakes it difficult to diffuse a metal component forming a lower wire 72(described later) into the resistance variable layer 76 and does notoxidize and reduce the resistance variable layer 76 is used for aconnection electrode 73. Below the connection electrode 73, the lowerwire 72 is provided using an electric conductor material made of, forexample, Al or Cu, which is generally used in a semiconductor process.

Between the resistance variable layer 76 and an embedded electrode 79, aconnection electrode 77 is provided in the same manner. The connectionelectrodes 73 and 77 may be formed of an electric conductor materialsuch as platinum (Pt), titanium nitride (TiN) or tantalum nitride (TaN),for example. Further, semiconductor layers 80, upper electrodes 81 andconnection electrodes 82 are provided in stripe shape such that they arerespectively connected to the embedded electrodes 79 and respectivelycross the lower-layer electrode wires 71. The connection electrodes 82are extended to outside the matrix region and connected to theupper-layer electrode wires (not shown). Alternatively, the connectionelectrodes 82 may serve as the upper-layer electrode wires. The otherconfiguration is identical to that of the nonvolatile semiconductormemory apparatus 10 of Embodiment 1 and will not be further described.

In such a configuration, memory portions 75 are each constituted by theresistance variable layer 76, a connection electrode 73 a and theembedded connection electrode 77 sandwiching the resistance variablelayer 76. The non-ohmic devices 78 which are comprised of MSM diodes areeach constituted by the embedded electrode 79 which is a metal electrodelayer, the upper electrode 81 and the semiconductor layer 80. Theembedded electrode 79 which is the metal electrode layer is embedded tofill the contact hole.

The feature of this embodiment is that the non-ohmic device 78 is theMSM diode in which the embedded electrode 79 and the upper electrode 81are formed of Al and the semiconductor layer 80 is formed of anitrogen-deficiency silicone nitride (SiNx) film. The SiNx film havingsuch a semiconductor property is formed by reactive sputtering in anitrogen gas atmosphere using, for example, a Si target. For example,the SiNx film is formed under the condition in which the temperature isa room temperature, the chamber pressure is 0.1 Pa to 1 Pa, and theAr/N2 flow rate is 18 sccm/2 sccm.

Alternatively, the embedded electrodes 79 and the upper electrodes 81may be formed of Pt instead of Al. In a case where SiNx having asemiconductor property was formed to have a thickness of 16 nm under theabove mentioned conditions, a current density of 2.5×10³ A/cm² wasobtained by applying a voltage of 1.6V and 5×10² A/cm² was obtained byapplication of a voltage of 0.8V. In a case where these voltages areused as a reference, an on/off ratio is 5. Thus, it was confirmed thatthe MSM diode is well operable as a non-ohmic device for use with thenonvolatile semiconductor memory apparatus.

Whereas in this embodiment, the connection electrodes 73 and 77 areprovided on the both surfaces of the resistance variable layer 76, thesemay be omitted. For example, depending on selection of the material ofthe resistance variable layer 76, the connection electrodes 73 and 77may in some cases are unnecessary. In this case, the nonvolatilesemiconductor memory apparatus 70 may be configured as in thenonvolatile semiconductor memory apparatus 10 of Embodiment 1.

(Embodiment 4)

FIG. 13 is a cross-sectional view showing a configuration of memoryportions 93 and non-ohmic devices 96 which are major constituents of anonvolatile semiconductor memory apparatus 90 according to Embodiment 4of the present invention. The feature of the nonvolatile semiconductormemory apparatus 90 of this embodiment is that a non-ohmic device 96 isconstituted by a p-n junction diode having a laminated-layer structureof a p-type semiconductor layer 97 and an n-type semiconductor layer 98.Furthermore, this embodiment has a feature in which the p-typesemiconductor layer 97 constituting the non-ohmic device 96 is embeddedto fill the contact hole together with the embedded electrode 95.Instead of the p-type semiconductor layer 97, the n-type semiconductorlayer 98 may be embedded together with the embedded electrode 95.

Memory portions 93 are each constituted by a resistance variable layer94, a lower-layer electrode wire 91 a and the embedded electrode 95sandwiching the resistance variable layer 94. The lower-layer electrodewires 91, an interlayer insulating layer 92 and upper electrodes 99 havethe same structures as those of the nonvolatile semiconductor memoryapparatus 10 of Embodiment 1. The upper electrodes 99 are connected tothe upper-layer electrode wires (not shown) outside the matrix region asin the nonvolatile semiconductor memory apparatus 10.

As a p-type semiconductor material forming the p-n junction diode, amaterial selected from, for example, ZnO, CdO, SnO₂, TiO₂, CeO₂, Fe₃O₄,WO₃, and Ta₂O₅ may be used. As an n-type semiconductor material, amaterial selected from, for example, Fe_((1-y)), O, NiO, CuO, Cu₂O, andMnO₂ may be used. In further alternative, p-doped silicon or n-dopedsilicon may be used.

In the present invention, instead of the MIM diode described inEmbodiment 1, the MSM diode described in Embodiment 3, or the p-njunction diode described in Embodiment 4, the non-ohmic device may be aschottky diode forming a schottky connection between a semiconductorlayer and an embedded electrode or a semiconductor layer and an upperelectrode, for example. In this case, the nonvolatile semiconductormemory apparatus may have a configuration which is similar to that ofthe nonvolatile semiconductor memory apparatus 10 shown in FIG. 1 or thenonvolatile semiconductor memory apparatus 70 show in FIG. 12. Note thatwhen the non-ohmic device is the schottky diode having a laminated-layerstructure formed by two layers which are the semiconductor layer and themetal electrode layer, it is necessary to embed the embedded electrodewhich is the metal electrode layer to fill the contact hole. Using sucha schottky diode, a configuration similar to that of the nonvolatilesemiconductor memory apparatus 40 having the laminated-layer structureshown in FIG. 11 is attainable.

When the non-ohmic device is the schottky diode, advantages as describedbelow are achieved. First, since the schottky diode is a majoritycarrier device unlike the p-n junction diode, accumulation of minoritycarrier does not occur, and thus the schottky diode enables thehigh-speed access. Second, since it is not necessary to form a p-njunction, a diode configuration is simple, and a manufacturing thereofis simplified. Third, the p-n junction has a problem associated with aproperty change depending on temperatures, but the schottky junction isstable with respect to temperatures, and can lessen a restriction suchas a heating condition during manufacturing steps.

Furthermore, for example, the p-n junction diode has a high forwardthreshold (about 0.5V), whereas the schottky diode having an interfacebetween, for example, titanium silicide and n-type silicon, has aforward threshold of 0.2V, and therefore makes it possible to suppressdisturb during reading or writing.

(Embodiment 5)

FIG. 14 is a cross-sectional view showing a configuration of memoryportions 103 and non-ohmic devices 106 which are major constituents of anonvolatile semiconductor memory apparatus 100 according to Embodiment 5of the present invention. FIG. 14( a) is a plan view. FIG. 14( b) is across-sectional view taken in the direction of arrows along line14A-14A. The nonvolatile semiconductor memory apparatus 100 of thisembodiment has basically the same configuration as the nonvolatilesemiconductor memory apparatus 10 of Embodiment 1, but has a feature inwhich each of an insulator layer 107 and an upper electrode 108constituting a non-ohmic device 106 is isolated for each memory portion103. For this reason, the upper-layer electrode wires 110 are providedin stripe shape on an interlayer insulating layer 109 embedded with thenon-ohmic devices 106 such that the upper-layer electrode wires 110 arerespectively connected to the upper electrodes 108 and respectivelycross the lower-layer electrode wires 101.

In such a configuration, since the upper-layer electrode wires 110 areprovided independently of the non-ohmic devices 106, they can berespectively made of optimal materials selected. In addition, a step forconnecting the upper-layer electrode wires 110 to the active elements(not shown) via the embedded conductors (not shown) inside the contactholes provided outside the matrix region can be simplified.

The memory portions 103 are each constituted by a resistance variablelayer 104, a lower-layer electrode wire 101 a and an embedded electrode105 sandwiching the resistance variable layer 104. The non-ohmic devices106 are constituted by a MIM diode including the embedded electrode 105which is the metal electrode layer, the upper electrode 108 and theinsulator layer 107. When the non-ohmic devices 106 are the MIM diodesas described above, an area of the diodes can be increased and theinsulator layers 107 can be thinned. Therefore, a current capacity canbe increased, and a variation in property can be reduced.

The non-ohmic device 106 is not limited to the MIM diode. By using thesemiconductor layer instead of the insulator layer 107, the MSM diode,the p-n junction diode or the schottky junction diode may be formed.Moreover, the nonvolatile semiconductor memory apparatuses of Embodiment3 to Embodiment 5 may have a laminated-layer structure as in thenonvolatile semiconductor memory apparatus of Embodiment 2.

Whereas in this embodiment, the non-ohmic device 106 is isolated foreach memory portion 103, it may be isolated for each set of pluralmemory portions 103.

Numerous modifications and alternative embodiments of the presentinvention will be apparent to those skilled in the art in view of theforegoing description. Accordingly, the description is to be construedas illustrative only, and is provided for the purpose of teaching thoseskilled in the art the best mode of carrying out the invention. Thedetails of the structure and/or function may be varied substantiallywithout departing from the spirit of the invention.

For example, in the above described embodiments, the resistance variablelayers are embedded to fill the contact holes, this is merely exemplary.The resistance variable layers may be formed by upper surface portionsof the lower-layer electrode wires so that they are positioned outsidethe contact holes, although this is not shown. In this case, electricconnection may be made between the resistance variable layers and thenon-ohmic devices using suitable electric conductors embedded to fillthe contact holes.

Industrial Applicability

A nonvolatile semiconductor memory apparatus of the present invention iscapable of simplifying a manufacturing method, of suppressing avariation in property of a non-ohmic device, of stabilizing a pressureresistance of the non-ohmic device, and of increasing a current capacityof the non-ohmic device, and therefore is useful in fields of a varietyof electronic hardware using the nonvolatile memory apparatuses.

1. A nonvolatile semiconductor memory apparatus comprising: a substrate;stripe-shaped lower-layer electrode wires provided on the substrate; aninterlayer insulating layer which is disposed on the substrate includingthe lower-layer electrode wires and is provided with contact holes atlocations respectively opposite to the lower-layer electrode wires;resistance variable layers which are respectively connected to thelower-layer electrode wires; and non-ohmic devices which arerespectively provided on the resistance variable layers such that thenon-ohmic devices are respectively connected to the resistance variablelayers; wherein the non-ohmic devices each has a laminated-layerstructure including plural semiconductor layers, a laminated-layerstructure including a metal electrode layer and an insulator layer, or alaminated-layer structure including a metal electrode layer and asemiconductor layer; and wherein one layer of the laminated-layerstructure is embedded to fill each of the contact holes and thesemiconductor layer or the insulator layer which is the other layer ofthe laminated-layer structure has a larger area than an opening of eachof the contact holes and is provided on the interlayer insulating layer.2. The nonvolatile semiconductor memory apparatus according to claim 1,wherein a plurality of constituent units, each of which includes theinterlayer insulating layer, the resistance variable layer, and thenon-ohmic device, are stacked to form a layer structure.
 3. Thenonvolatile semiconductor memory apparatus according to claim 1, whereinthe other layers of the laminated-layer structures respectively formingthe non-ohmic devices are provided in stripe shape on the interlayerinsulating layer so as to respectively cross the lower-layer electrodewires.
 4. The nonvolatile semiconductor memory apparatus according toclaim 1, further comprising: stripe-shaped upper-layer electrode wireswhich are provided on the non-ohmic devices such that the upper-layerelectrode wires are respectively connected to the non-ohmic devices andrespectively cross the lower-layer electrode wires.
 5. The nonvolatilesemiconductor memory apparatus according to claim 1, wherein thenon-ohmic devices are MIM diodes each having a laminated-layer structureincluding three layers which are an insulator layer and metal electrodelayers sandwiching the insulator layer, and the metal electrode layerwhich is closer to the resistance variable layer is embedded to filleach of the contact holes.
 6. The nonvolatile semiconductor memoryapparatus according to claim 1, wherein the non-ohmic devices are MSMdiodes each having a laminated-layer structure including three layerswhich are a semiconductor layer and metal electrode layers sandwichingthe semiconductor layer, and the metal electrode layer which is closerto the resistance variable layer is embedded to fill each of the contactholes.
 7. The nonvolatile semiconductor memory apparatus according toclaim 1, wherein the non-ohmic devices are p-n junction diodes eachhaving a laminated-layer structure including two layers which are ap-type semiconductor layer and an n-type semiconductor layer, and thep-type semiconductor layer or the n-type semiconductor layer is embeddedto fill each of the contact holes.
 8. The nonvolatile semiconductormemory apparatus according to claim 1, wherein the non-ohmic devices areschottky diodes each having a laminated-layer structure including twolayers which are a semiconductor layer and a metal electrode layer, andthe metal electrode layer is embedded to fill each of the contact holes.